Fixes an issue in which the allocation health watcher was checking for
allocations health based on un-interpolated services and checks. Change
the interface for retrieving check information from Consul to retrieving
all registered services and checks by allocation. In the future this
will allow us to output nicer messages.
Fixes https://github.com/hashicorp/nomad/issues/2969
This PR adds watching of allocation health at the client. The client can
watch for health based on the tasks running on time and also based on
the consul checks passing.
